An exhaust fluid treatment apparatus may comprise a plurality of modules, wherein each module is intended to treat one or more constituents of an exhaust fluid. The modules may be arranged in series such that exhaust fluid flows through each module in sequence.
An exhaust fluid treatment apparatus may comprise a diesel oxidation catalyst module, a diesel particulate filter module downstream of the diesel oxidation catalyst module and/or a selective catalytic reduction module, downstream of the diesel particulate filter module.
It may be appropriate to perform periodic checks on individual modules of the exhaust fluid treatment apparatus to ensure that the individual modules are performing as expected. This may be particularly important if unexpected performance of a module earlier in the fluid flow path may have an effect on performance of modules which are located later in the fluid flow path.
For example, unexpected performance in the diesel oxidation catalyst can result in reduced oxidation of hydrocarbons in the diesel oxidation catalyst. This, in turn, may mean that the fluid output from the diesel oxidation catalyst has a lower temperature than expected and/or desired. Such unexpected performance may also result in emission of unburnt fuel to atmosphere. Unexpected performance in the diesel oxidation catalyst may arise as a consequence of deposits, such as sulphurous deposits, collecting on the catalytic surfaces of the diesel oxidation catalyst. A reduced temperature of fluid output from the diesel oxidation catalyst can result in unexpected performance of a diesel particulate filter located downstream of the diesel oxidation catalyst since, at lower temperatures, carbon entering the diesel particulate filter in the form of soot is less likely to oxidise in the diesel particulate filter. Lower temperatures can also effect performance in a selective catalytic reduction module located downstream of the diesel particulate filter.
It is known to inject fuel into the diesel oxidation catalyst for combustion therein, for example to increase temperature in the diesel oxidation catalyst or to cause particular constituents within the diesel oxidation catalyst to be combusted. For example, it may be desirable to desulphate the exhaust fluid treatment apparatus or to remove deposits therefrom. It may be undesirable, however, to inject fuel into the diesel oxidation catalyst where the fuel may pass through the diesel oxidation catalyst without combusting. It may, therefore, be appropriate to check performance of a diesel oxidation catalyst in order to ensure that injected fuel combusts as expected.
Against this background, there is provided a method for checking operation of the diesel oxidation catalyst module.